Technical Field
The present invention relates to a stator for a rotating electric machine mounted in a vehicle or the like and used as an electrical motor or a generator.
Related Art
A rotating electric machine to be mounted in a vehicle is generally known that includes a rotor, a stator core including a plurality of slots radially opposing the rotor and arranged in a circumferential direction of the core, and a stator having a stator winding formed of a plurality of phase windings wound through the slots of the stator core.
Japanese Patent Application Laid-Open Publication No. 2005-110361 discloses techniques for an armature (or the stator) for the rotating electric machine that can provide larger currents and simplify lead outs and connecting lines. Japanese Patent Application Laid-Open Publication No. 2005-110361 discloses a stator winding formed of three phase windings (U-, V-, and W-phase windings) lap wound around the stator core by welding or bonding given pairs of open end portions of a plurality of conductor segments inserted in the slots of the stator core on one axial coil end. Each phase winding of the stator core is formed of a parallel connection of four parallel windings. Japanese Patent Application Laid-Open Publication No. 2005-110361 further discloses that an X-phase winding is evenly wound in each pair of circumferentially adjacent X-phase slots (for X=U, V, W).
Japanese Patent Application Laid-Open Publication No. 2014-96857 discloses techniques for a stator having multiple double slots, i.e. a plurality pairs of circumferentially adjacent pairs of slots in a distributed winding structure, capable of preventing circulating current from occurring between parallel windings. Japanese Patent Application Laid-Open Publication No. 2014-96857 discloses a stator winding formed of multiple phase windings wave wound around the stator core, each phase winding of the stator winding is a parallel connection of a plurality of parallel windings of the same phase. Japanese Patent Application Laid-Open Publication No. 2014-96857 further discloses a technique of switching between the first and second slots belonging to different pairs upon transition from one layer to another layer.
The stator winding disclosed in Japanese Patent Application Laid-Open Publication No. 2005-110361 is configured such that given open end portions of the plurality of U-shaped conductor segments are welded to each other. Each slot therefore receives an even number of slot-received portions of conductor segments radially aligned in a column. The plurality of U-shaped conductor segments include outer and inner conductor segments. The outer conductor segments are inserted in the first and fourth layers of the slots, and the inner conductor segments are inserted in the second and third layers of the slots.
The outer and Inner conductor segments are normally arranged at six slot intervals (or at a six slot pitch), where, as shown in FIG. 17, each outer conductor segment 72 straddles one of the Inner conductor segments 71, which leads to overlap of conductor segments.
Five slot pitch based switching and seven slot pitch based switching are provided so that the phase winding can switch between the first and second slot groups, which, however, may give rise to a disadvantage that an outer conductor segment 72A inserted in the first and fourth layers of the slots that are five slots away from each other straddles the normal inner conductor segment 71 inserted in the second and third layers of the slots that are six slots away from each other. Further, as shown in FIG. 18, an outer conductor segment 72B inserted in the first and fourth layers of the slots that are seven slots away from each other may further straddle the outer conductor segment 72A. Such triple overlap may increase an axial length of the coil end portion of the stator winding.
It can be envisaged that when slot-received portions of six conductor segments are inserted in slots radially aligned in a column, first conductor segments 75 to be inserted in the third and fourth layers of the slots, second conductor segments 76 to be inserted in second and fifth layers of the slots, and third conductor segments 77A, 77B to be inserted in first and sixth layers of the slots may be used. The third conductor segment 77A is to be inserted into the first and sixth layers of the slots that are five slots away from each other. And the third conductor segment 77B is to be inserted into the first and sixth layers of the slots that are seven slots away from each other. This may give rise to a disadvantage that the second conductor segment 76 straddles the first conductor segment 75, the conductor segment 77A straddles the second conductor segment 76, and the conductor segment 77B straddles the third conductor segment 77A, as shown in FIG. 19. Such quadruple overlap may further increase an axial length of the coil end portion of the stator winding.
In consideration of the foregoing, exemplary embodiments of the present invention are directed to providing a stator for a rotating electric machine capable of completely preventing circulating current from occurring between parallel windings of each phase winding while preventing an axial length of a coil end portion from increasing.